The present invention relates to a washing machine, and more particularly to an electronically-controlled washing machine with a reservation function capable of reserving in advance a time at which a washing operation terminates.
A conventional electronically-controlled washing machine is disclosed, in for example Automation Technology (No. 12, Vol. 6, 1980) wherein when washing starts, a power switch is turned on to supply an electric power to a control unit and a load unit such as an agitating means, a water supply means, a water discharge means, a clutch change-over means, a softening and finishing agent charge means or the like. In the conventional washing machine, the supply of the electric power is continued even when a washing operation terminates unless the power switch is turned off by an operator.
In particular, washing machines with a reservation function are generally kept connected to a commercial power supply. With such a washing machine, even if a power switch is turned off, the commercial power supply is kept applied to the control unit although it seems that the commercial power supply has been completely cut off because an indicator lamp has gone off, a key input is prohibited from being acquired and an output for driving a load is prohibited.
In particular, it is typical that the commercial power supply is applied to the load unit and a power of 5-10 V is supplied to the control unit during a waiting period from the time a reserved operation is set to the time at which the operation actually starts.
The above stated conventional washing machine has disadvantages such as those shown below because the commercial power supply is applied to the load unit during a time at which the washing machine is not actually operated.
1. A malfunction of the load unit due to the deterioration of semiconductor switching elements such as TRIACs or the like which serve as switches to drive and to stop the load in response to a signal from an instruction and control unit, the semiconductor switching elements deteriorating in accordance with an application being supplied with electric power for a long time.
2. An unexpected abnormal operation of the washing machine which occurs when external noise reaches the instruction and control unit by passing through the commercial power supply and the atmosphere. This causes the instruction and control unit to malfunction or to get out of control.
3. An abnormal operation of the washing machine or an electric shock due to leakage of the semiconductor switching elements and the load unit caused by water attached thereto or the corrosion or the deterioration thereof.
As described above, in the conventional washing machine there is a lack of attention to safety when washing machines are used.